The present invention relates to medical electrical stimulators, such as Spinal Cord Stimulation (SCS) systems and more particularly to methods for efficiently selecting electrode configurations. An SCS system, used herein as an example of a medical electrical stimulator of the invention, treats chronic pain by providing electrical stimulation pulses through the individual contacts (a.k.a., electrodes) of an electrode array (a.k.a., a lead) placed epidurally next to a patient's spinal cord. The combination of stimulation pulses delivered to the electrodes of an electrode array constitutes an electrode configuration. In other words, an electrode configuration represents each polarity, being positive, negative, or zero of each of the electrodes. Other parameters that may be controlled or varied in SCS and other forms of medical electrical stimulation are the frequency of pulses provided through the electrode array, pulse width, and the strength (amplitude) of pulses delivered. Amplitude maybe measured in milliamps, volts, etc. In some SCS systems, the “distribution” of the current/voltage across the electrodes may be varied such that the polarity of each electrode is not a whole number value, but represents a fraction of positive or negative values. Moreover, there may be some electrodes that remain inactive for certain electrode configurations, meaning that no current/voltage is applied through the inactive electrode(s). Therefore, for such systems, each electrode configuration also represents a polarity percentage of each active electrode of an electrode array.
Previous SCS technology identified these parameters and effectuated stimulation through an electrode array or lead at specific electrode configurations. However, previous SCS technologies attempted to evaluate parameters, including electrode configuration, strength, pulse width, etc., one at a time. An optimized stimulation parameter set for a specific patient may be determined from the response of the patient to various sets of stimulation parameters. There is, however, an extremely large number of possible combinations of stimulation parameters, and evaluating all possible sets is very time consuming, and perhaps impractical.
Spinal cord stimulation is a well accepted clinical method for reducing pain in certain populations of patients. An SCS system typically includes an Implantable Pulse Generator (IPG), electrodes, electrode lead, and, if needed, one or more electrode lead extensions. Some systems, rather than using an IPG, include an implanted Radio-Frequency receiver that receives pulses from an external transmitter. In either case, the electrodes are implanted along the dura of the spinal cord, and the IPG generates electrical pulses that are delivered, through the electrodes, to the dorsal column and dorsal root fibers within the spinal cord. Individual electrode contacts (the “electrodes”) are arranged in a desired pattern and spacing in order to create an electrode array. Individual wires within one or more electrode leads connect with each electrode in the array. The electrode leads exit the spinal column and generally attach to one or more electrode lead extensions or, depending on the length of the leads, they may attach directly to the IPG. The leads and/or lead extensions are typically tunneled around the torso of the patient to a subcutaneous pocket where the IPG is implanted.
Spinal cord stimulators and other stimulation systems are known in the art. For example, an implantable electronic stimulator is disclosed in U.S. Pat. No. 3,646,940 issued Mar. 7, 1972 for “Implantable Electronic Stimulator Electrode and Method” that provides timed sequenced electrical impulses to a plurality of electrodes. As another example, U.S. Pat. No. 3,724,467 issued Apr. 3, 1973 for “Electrode Implant For The Neuro-Stimulation of the Spinal Cord,” teaches an electrode implant for the neuro-stimulation of the spinal cord. A relatively thin and flexible strip of physiologically inert plastic is provided as a carrier on which a plurality of electrodes are formed. The electrodes are connected by leads to an RF receiver, which is also implanted.
In U.S. Pat. No. 3,822,708, issued Jul. 9, 1974 for “Electrical Spinal Cord Stimulating Device and Method for Management of Pain,” another type of electrical spinal cord stimulation device is taught. The device disclosed in the '708 patent has five aligned electrodes, which are positioned longitudinally on the spinal cord. Electrical pulses applied to the electrodes block perceived intractable pain, while allowing passage of other sensations. A patient-operated switch allows the patient to adjust the stimulation parameters.
Electrode arrays currently used with known SCS systems may employ between one and sixteen electrodes on a lead or leads. Electrodes are selectively programmed to act as anodes, cathodes, or left off, creating an electrode configuration. The number of electrode configurations available, combined with the ability of integrated circuits to generate a variety of complex stimulation pulses, presents a huge selection of stimulation parameter sets to the clinician. When an SCS system is implanted, a “fitting” procedure is performed to select an effective stimulation parameter set for a particular patient. Such a session of applying various stimulation parameters and electrode configurations may be referred to as a “fitting” or “programming” session. Additionally, a series of electrode configurations to be applied to a patient may be organized in a steering table or in another suitable manner.
A known practice is to manually test one parameter set, and then select a new stimulation parameter set to test, and compare the results. Each parameter set is painstakingly configured and increased in amplitude gradually to avoid patient discomfort. A clinician often bases his selection of a new stimulation parameter set on his/her personal experience and intuition. There is no systematic method to guide the clinician. If the selected stimulation parameters are not an improvement, the clinician repeats these steps, using a new stimulation parameter set, based only on dead-reckoning. The combination of the time required to test each parameter set, and the number of parameter sets tested, may result in a very time consuming process. For instance, a system with 16 selectable electrodes contains over 40 million possible combinations of electrode configurations alone. Thus, testing all possible combinations is impractical.
In order to achieve an effective result from spinal cord stimulation, the lead or leads may be placed in a location such that the electrical stimulation will cause paresthesia. The paresthesia induced by the stimulation and perceived by the patient should be located in approximately the same place in the patient's body as the pain that is the target of treatment. If a lead is not correctly positioned, it is possible that the patient will receive little or no benefit from an implanted SCS system. Thus, correct lead placement can mean the difference between effective and ineffective pain therapy.
In order to test the effectiveness on a particular patient of various stimulation parameters and electrode configurations, it is necessary to provide a series of stimulation parameters in a systematic method. Several such systems exist including the systems disclosed in U.S. Pat. No. 6,393,325, herein incorporated by reference in its entirety, wherein a patient may direct the movement of the stimulus current through a suitable interface.
Another method of testing the effectiveness of various stimulation parameters is disclosed in U.S. application Ser. No. 11/026,859, herein incorporated by reference in its entirety. In this Application, during a fitting session with a patient, a clinician uses navigation with two parameter tables to step through and optimize stimulation parameters.
The inventors have ascertained that improved methods are needed for selection of electrode configurations during navigation through a programming session, whereby each patient may efficiently optimize and personalize his/her stimulation treatment in terms of stimulation strength, pulse rate, pulse width, and electrode configuration.